The present invention relates to the field of electronic image display and more particularly to an improvement in the optical fiber coding method and apparatus of a radiation image amplifier.
Radiation image amplifiers are designed to detect patterns of radiation of relatively weak intensity, code the image of the pattern in the form of electrical signals, amplify such signals and present an enlarged and intensified visual display of the original radiation pattern. Such radiation image amplifiers locate the incident radiation by stopping the radiation in a scintillator. The light emitted at the location of the radiation stopped in the scintillator is transferred via an optical fiber array to photosensitive amplifiers such as photomultiplier tubes for conversion into electrical signals. The resulting electrical signals are further amplified to obtain the desired visual display. Such a radiation image amplifier has been described in U.S. Pat. No. 3,652,855 which issed Mar. 28, 1972 to McIntyre and Saylor and which is incorporated herein by reference for all purposes.
The image transmission section of a radiation image amplifier typically comprises an array of optical fibers optically coupled at one end to a scintillator and optically coupled at the other end to a bank of photomultiplier tubes. The fibers transmit light from the scintillator to the photomultipliers. The number of photomultipliers required to locate a particular scintillation can be minimized by utilizing an optical fiber coding method for matrixing the fibers with different photomultipliers.
The proper matrixing is accomplished by positioning the fibers with their input ends arranged in a matrix with one or more fibers covering each unit area of the field of the image to be detected. Each of the individual fibers in a given unit area is connected to a different photomultiplier tube, but fibers from different areas are connected to the same photomultiplier tubes in different combinations. With a matrix coding method, a large number of scintillation locations can be determined from a small number of photomultipliers. Such a matrix coding method has been described in U.S. Pat. No. 3,652,855.
Because many individual optical fibers must be used to make up a matrix and because the fibers are relatively expensive to install, it is desirable to minimize the number of fibers necessary to provide a radiation image. Since the level of image resolution is proportional to the number of fibers in the matrix, a reduction in the number of fibers used naturally impairs the resolution attainable. The existing problem is to attain an increased level of image resolution in a radiation image amplifier without a corresponding increase in the number of optical fibers in the fiber matrix. Stated alternatively, the problem is to reduce the number of optical fibers in the fiber matrix of a radiation image amplifier without a corresponding decrease in the image resolution attainable by said amplifier.
Radiation image amplifiers may be used as detectors in numerous applications. In particular, radiation image amplifiers have been used as real time detectors of gamma ray radiation for the stereoscopic viewing of annihilation radiation sources as described in U.S. Pat. No. 4,135,089 which issued Jan. 16, 1979 to McIntyre. In such an application, the timing signal that is produced by the radiation image amplifier to indicate when each gamma ray is detected is used to determine the correlations between points associated with pairs of gamma rays. The rate at which such information may be processed is limited by the time resolution of the radiation image amplifier. Specifically, the more rapidly the radiation image amplifier can detect incident radiation the more effectively can accidental coincidence pulses be rejected.
Since the photomultipliers of a radiation image amplifier must obtain at least one photoelectron from a scintillation in order to detect a gamma ray, the time that is required to obtain that photoelectron is inversely proportional to the amount of light incident on the photomultipliers.
The existing problem is to reduce the time required by a radiation image amplifier to detect incident radiation and thereby increase the time resolution attainable by said amplifier in order to permit increased rates for processing radiation image data.